Rotatable wave guide attenuator



` A July 15, 41952 A. E. BOWEN I vROTATBLE WAVE GUIDE ATTENUATOR Filed Dec. l1, 1946 N .mi Y 5 IIIIILIII k IIL N Mw l N0. WB m5 l ATTORNEY Patented July 15, 1952 UNITED STATES Param" ori-Ica -ROTATABLE WAVE GUIDE ATTENUATOR Arnold E. Bowen, Fair Haven, N. J., assigner to Bell Telephone Laboratories, Incorporated, New York,- N. Y., a corporation of New York Application December 11A, 1946, Serial No. 715,587 i 8 Claims. (Cl. 178-44) This invention relates to variable wave guide attenuators.

An object of the invention is to attenuate electromagnetic waves by means offrotatable wave guide sections without alteringlthe polarization direction. l

Another object is to effectively suppress quadrature polarizations developedin rotatable wave.

guide attenuators.

A feature of the invention is a rotatable -attem uator for linearly polarized waves,l characterized by sections of waveguide provided with diametral absorber rods and conductive reflecting septa for enhancing the absorption of cross-components.

Another feature of the invention is a tapered impedance matching section between a rectangular and cylindrical wave guide. y f

Another feature of the inventionis a quadrature polarization suppressor comprising a section of rectangular guide interposed between a pair of cylindrical pipe sections.

Referring to the figures of the drawing:

Fig. 1 shows a rotatable attenuator for bilateral or two-way transmission in accordance with the invention;

Fig. 1A is an end view thereof Fig. 2 represents a modification; f

Fig. 2A is an end view thereof; and

Fig. 3 is another modification of the attenuator.

Rotatable wave guide attenuators, adapted to continuously attenuate anelectromagnetic wave as a function of the angle of rotation of a wave guide section, without altering its polarization direction, have been disclosed in the United States application of A. E. Bowen, Serial No. 715,589, led concurrently herewith;y The attenuation a. of the rotatable attenuator disclosed therein varies as a cosine squaredk function of the angle 0.

In accordance with the teachings of the aforementioned Bowen application, a wave'may'be attenuated without altering the direction of its polarization, by means of relatively 'rotatable wave guide sections, provided with Suppressors for quadrature polarizations.' t v In accordance with embodiments of thepresent invention, undesired cross-components and quadsepta and terminating rod absorbers, or by polar,- ization suppressive rectangular pipe sections.

In one exemplary embodiment thereof, the rotatable attenuator may'compriseay rotatable section of Wave guide B intermediate two stationary wave guide sections A, C'. respectively, wherein the wave guide section B maybe provided with a pair of spaced power absorbing rods placed symmetrically on opposite sides of'v a conductive, reiiecting septum. `'Ifhestationary guide sections A, C are provided withk quadrature polarization Suppressors, which may take various forms, such aspolarizing sections of rectangular wave guide, combinations of septa and rods, or the like.

When guide sections A, B, C are oriented with absorbing rods and reflecting septa in a common plane perpendicular'to the polarization of the incomingwave, a reference condition is established, characterized by zero attenuation.

As the rotatable sectionB is rotated through an angle 0, the wave may be made to emerge from the systemA, B, C with its amplitude reduced as a function of 0, and with polarization direction unchanged. Components with quadrature polarizations existing before or arising during the rotation are extinguished by the suppressors, namely, the conductive septa and absorber rods, or the rectangular pipe Suppressors in various combinations.

The attenuators A, B, C in accordance with the invention are Iby' symmetry adapted for bilateral or two-way transmission, although for unilateral or one-way'wave transmission, reduction of parts may be achieved by the omission of one of the stationary sections A, C.

A rotatable attenuator in accordance with an embodiment of the invention, is illustrated in Fig. 1, wherein airotatable wavew guide, section B is coupled to a pair of stationary guide sections A, C, respectively, by means of the rotatable joints shown whereby waves propagated bilaterally may be attenuated without altering the direction of polarization.

The rotatable section B is a cylindrical pipe or wave guide section provided with a pair of dirature polarizations may be effectivelysuppressed in a rotatable attenuator by combinations of ametral, absorber rods I, I', positioned a'distance on opposite sides of a conductive, coplanar reflecting septum 2 (where M is the wavelength in e* able attenuator, illustrated nf Fiel isessen-' o derived .fiom

the guide). The conductive septum 2 is a. thin,

'metallic plate, preferably in lengthv or greater, which acts as a perfect reilector for Waves, polarized parallel to its plane.

, The handle .3 is formanually rotating guide secfo'rm a diametral absorber 4, Which may be a resistance wire, or the like. In li'eu .of absorbing rods I 4. I', attenuating platesasdisclosed in they i li at maybeused;

@The basic principle of ope 4n Qi the ro tiauy similar to that described nl the alf-rementioned application 'of A'E. Bowen.

When the wave guide sections A, B, C are oriented. withtlieir attenuating rods and condito- Ytive 4sepia ooplaiiar. iiiooiiiiiie l E with Polarization,*Perpeiidioular io the. vooiiiiiioii plane.

j Will pass freely throughfthersystemeapqremerge vnaffeoied iii its, polarization jvetpr; an@ a, p11- -tuoie- Y, i Y Y As the rqtat'abiefsetien B is rotated ,through ananglev a relativeto thefstatonary sectionsA, C,

the. amplitude 'ofthe emergentwave E Will'be reduced.' aseos? o .ias e explained greater detail in. the aforementioned United States applicatien oi A- E Bow-aah ,with its polarization veoior lioohanaed. Y

Iii the-terminology ofY the explanatory vector diagrams disclosed iiiereiii,- an iiiooiiiirig Wave (E) will pass freely through seoiionA, unaffeoied by'septum 5 ,andl Vabsorber rod 4 therein, Whose common-plane is,v perpendicular thereto. VIn its passagethroiieh therotated saisie. seotioia Bi, the wave veotor; may; be .ooiisidered as iesolvedinio quadrature oeiiipoaents Y atea ees; @and aaai; sa o j with respeoi to the septum as 'desoifibed'iii the aforementioned o-wen application. The comd por-lect Ei passes freely through. Section B, while the parallel component E11 kis reilecte'd hy cone' Vductive septum Tand fully kabsg'rloed-hy absorber rodi, ,The other rod l aots Simiiaiii'foii'a Wave propagating iii the opposite, direotioii- Y The .eompoiieiit El; ailier Passaseiiiiooeh cuide seetioii. Vliiseiifise resolvalole inie'two' quadratureooiiiaoiieiiia- .Qiie ooiaaoiient .E, =..;Ei ooS fi y beine perpendicolari@ theflolane of ,septum 5 and absorber rod. .-4,1 Passes freely v,'dieiiaoifei and emerges with,thesanie'direction of polarization as theriiiout-Wave lTiie-oiiieifoomlooiierit rioe'iiita parallel toseptum sorbed by rodd. Y

The relationship of .the amplitude -EL of the emergent Wave and E of the inputwave may be fi.' is yreflected 'thereby falliti..v a

The attenuation YE l a (1n decibels) :20 logm=20 logw m 5 TheV values of a, vs. 0 may .he tabulated as follows:

Irr summary, the effect of Y the rotatable attenuator A', BC on an input Wave E is to introduce a transmission loss therein proportional to cos2 0, where@ is the angle through Which section B has been rotated. The direction of polarization vrof the emergent wave, after a discrete or a continuoua, rotation oi .Section ;B. .Wi11 loe uiioiiaiieed with reference tov the input polarization of vector E.Y y l The 'rotatable aiteriiiator A, la.v` C disclosed in 3.0 Eig., 1 operatesbilaieialiy, loioduoiiis bx itsY Symmetry the same'- effects on Waves traveling in op-` p-osite eliieoiioiis. liiiiiilaieiaiiraiiiiiii only. Y for example, iroioiiahtgilo lett is. des veet the attenuator'can be simplified by therornn/sion. of guide section C ariel absorber jrod i! Y f in; the, ,rotatable aiieiioaior fiala Q. illustrated iii'iiia 2. Seeiioiie A., C eaoii ooiiiori'se aA aoiiabii.' Proportioneel aeoiioii of reoiaiiaular 'eu'iie '|50 which replaces conductivev septumd-of Figjfl and an absorber rod 4' located round waveguide Il joined to vI0 atY junction J.Y`I`he rectangular guide I0 is so dimensionecl as ,to transmit' watjes of the dominant Wave 'polarization' and tovac't as a cut-oi for the' quadrature polarization, i. e.,

Y and where a, b are'the sides of the rectangular crosssection (Fig. 2A) andais vthe free' space uayelength. Variable reactance screWsS 'an'df-S"A Y'are provided in the respective .rectangular pipes!!! to compensate for impedance discontinuities" at the junctions J, J f as disclosedi'n said concurrently filed Bowen application; vRotata'hle section B is identical with thefcor'respondingB guidof Fiel. Y Y v The operation of thedevice (Fig..2) Lis essentially similar to that described 'for'.'rf'ig 117th@ reotaiieiilar guides l0 beine incapable of trans: mittiiis oioaofooiiiooiieiits or the cuadratura polarizations. The input vector E will, hou/euer, ireel-i paas ,iiiroiiaiiaeeiion A, ae aeiea oii'ii'f B.; and C as previo sly V'firib'ft' and/emerge Vas Ea'oosi'@ and wiiiiiia poiaraatioii vee tenuator is shown in Figz '3. In thi pression ofthe rolssflco f" l im n A n" t polarizations is Wholly' by the'rectangular pipes;V as -di'sc osed 1n Vrco Stationary sections A, C of the rotatable attenuator A, B, C (Fig. 3) each comprise a rectangular wave guide I.2 for Ipassing the input wave E, with its polarization vector perpendicular to a, and a round wave guide I3 connected thereto by a tapered impedance matching transformer section I4.

The intermediate, rotatable section Bl comprises a piece of rectangular guide I5 joining together a pair of circular pipe sections I6, in which diametral attenuating plates I'I, I'I'. with impedance matching terminals are fastened. Each of the attenuators I'I-I1 is of the structural type more fully disclosed in the United States applications of A. E.` Bowen, Serial No. 486,013, led May 7, 1943, now Patent No. 2,600,466, and W. H. Hewitt, Jr., Serial No. 551,040, filed August 24, 1944, with impedance matching terminals of notched or tapered form. The reactance screw S may be adjusted to compensate for impedance discontinuities at junctions J, J

The circularpipes I3 of sections A, C are connected :by rotatable joints to the corresponding round pipes I6 of section B.

The operation of the embodiment, shown in Fig. 3 is as follows:

As previously explained, the rectangular guide I2 passes only polarizations perpendicular to its long side a while quadrature polarizations are cut off. The section B, having been rotated through an angle 0, permits a resolution of vector E into two components, E1 and E11, with respect to the plane of attenuating plates I'I, I'I. E11, which lies parallel to plate I'I, is attenuated thereby, while E1 passes freely thereover and through rectangular guide I5, which concomitantly cuts oft' and prevents the propagation 0I E11.

Component E1 also passes freely over attenuating plate I1' into section C, where it may be resolved into quadrature components.

One of these components, namely, E', which is perpendicular to a side a of the output rectangular guide I2 (on C), emerges as the output wave, with polarization parallel to the original vector E but amplitude reduced to E cos2 0, where 0 equals angle of rotation aforementioned. The other, which is a cross-component, is cut off by the action of the rectangular guide I2 of section C and thereby prevented from appearing in the output.

What is claimed is:

1. A rotatable attenuator comprising three wave guide sections, the intermediate section being rotatable and provided with a reflecting septum and a coplanar absorber rod.

2. A wave guide attenuator, comprising a rotatable section of wave guide, a conductive septum in length therein adapted to freely pass waves of one polarization and reflect waves of the quadrature polarization, and a coplanar attenuator spaced :from said septum and adapted to absorb the quadrature polarization.

3. A wave guide attenuator comprising relatively rotatable wave guide sections, one thereof containing a conductive septum and a pair of coplanar attenuators symmetrically disposed with respect to and spaced from said septum whereby waves polarized parallel thereto may be extinguished.

4. A wave guide attenuator comprising three cylindrical wave guide sections, the intermediate one being relatively rotatable with respect to the end sections, each section being provided with a diametral reiiecting septum and a coplanar absorber rod spaced therefrom, whereby waves polarized parallel thereto are suppressed.

5. An attenuator for microwaves comprising three wave guide sections, the intermediate wave guide section being rotatably connected to the end sections respectively, each wave guide end section having a polarizer for passing a desired polarization and suppressing the quadrature polarization, said sections adapted to be aligned to provide zero attenuation, an asymmetrical absorber in the intermediate section adapted to be rotated therewith whereby the amplitude of an input wave is attenuated as a function of the rotational position of said intermediate section, said polarization being unchanged in the attenuated wave.

6. The structure of claim 5, wherein the end sections are cylindrical pipes and the intermediate section contains a rectangular pipe adapted to pass waves polarized parallel to one face thereof and to cut off waves of the quadrature polarization. y

7. The structure of claim 5, wherein each end section comprises a cylindrical pipe connected to its respective polarizer and a tapering impedance transformer between said pipe and polarizer.

8. The structure of claim 5, wherein the intermediate section is provided with a polarization suppressor comprising a rectangular pipe and said absorber comprises coplanar attenuators spaced on opposite sides thereof.

ARNOLD E. BOWEN.

REFERENCES CITED The following references are of record in the rile of this patent:

UNITED STATES PATENTS Number Name Date 2,088,749 King Aug. 3, 1937 2,106,768 Southworth Feb. l, 1938 2.129.712 Southworth Sept. 13, 1938 2,197,122 Bowen Apr. 16, 1940 2,257,783 Bowen i-Oct. 7, 1941 2,407,267 Ginzton Sept. 10, 1946 2,423,130 Tyrrell July 1, 1947 2,423,383 Hershberger July 1, 1947 2,425,345 Ring Aug. 12, 1947 2,427,100 Kihn Sept. 9, 1947 2,433,368 Johnson Dec. 30, 1947 2,438,119 Fox Mar. 23, 1948 FOREIGN PATENTS Number Country Date 503,467 Great Britain Apr. 6, 1939 OTHER REFERENCES Proceedings of the I. R. E., October 1946, page 

